An experimental and theoretical investigation into the heat transfer of a finned water wall tube in a circulating fluidized bed boiler

Heat transfer improvement in a water wall tube with fins was investigated i n a circulating fluidized bed (CFB) boiler. Experiments were first conducte d in a 6 MWth CFB boiler then a model was developed to analyse and interpol ate the results. Temperatures at some discrete points within the wall cross -section of the tube were measured by burying 0.8 mm thermocouples within a tube. Experimental data showed an increase in heat absorption up to 45 per cent. A good agreement between measured and predicted values was noted. The distribution of temperature in the metal wall and of heat flux around t he outer wall of a tube with longitudinal and lateral fins was analysed by numerical solution of a two-dimensional heat conduction equation. Effects o f bed-to-wall heat transfer coefficient, water-to-tube inside heat transfer coefficient, bed temperature, water temperature and thermal conductivity o f the tube material on the heat flux around the water tube are discussed. T he present work also examines the influence of the length of the longitudin al fin and the water tube thickness. Heat flux was highest at the tip of th e longitudinal fin. It dropped, but increased again near the root of the la teral fin. Copyright (C) 2000 John Wiley & Sons, Ltd.